IMPROVEMENTS IN OR RELATING TO DEINKING OF PAPER

Abstract: The invention discloses various methods for separation of laser and xerographic printed paper waste containing ink having a magnetic component from other paper waste products containing ink which does not contain any magnetic material, by the use of at least one magnet. The invention also provides a method for removal of magnetic ink from pulp stock formed from such xerographic and laser printed paper waste comprising feeding such pulped paper waste past at least one magnet for removal of all or substantially all of such magnetic ink. The magnetic ink can be removed by capture or deflection techniques. The preferred magnetic force to be applied in order to achieve the required results, utilises background magnetic fields in excess of 4000 Gauss and a field gradient in excess of 1000 Gauss/cm. The invention also provides a method for improving the recyclability of paper waste having ink thereon which does not normally contain a magnetic component, by utilising one or more magnetic carriers in the formulations of the printing ink utilised. Also disclosed is a method of enabling adhesive material to be removed from paper pulp containing same comprising incorporating a magnetic filler or carrier in said adhesive and removing such adhesive by magnetic means.

Description: IMPROVEMENTS IN OR RELATING TO DEINKING OF PAPER The present invention concerns improvements in or relating to the dein ing of paper. More particularly, the present invention is concerned with the recovery of paper for recycling purposes, which paper has all traces, or substantially all traces, of ink removed therefrom. More particularly, the invention is concerned with the recycling of high quality white paper utilised in the production of recycled photocopier and laser print paper. In recent times, more and more attention is being given to the recycling of paper and paper products in an attempt to reduce the amount of virgin pulp which is utilised in paper production. In order to ensure that the recycled paper is of the desired quality, it is generally required to remove all, or substantially all, of the print from the paper and paper products to be recycled. This is particularly the case in connection with laser and xerographic printed papers. In the paper industry, such papers are normally of high quality white paper and are normally regarded as a potentially extremely valuable feedstock to make recycled copier and laser print paper. However, to date, the conventional method adopted for deinking such papers has not been particularly successful. Chemical extractant techniques, such as flotation and the use of dispersion aids have primarily been used in this regard. There are two main issues surrounding the economic recyclability of such laser and xerographic printed papers. Firstly, when paper and paper products are collected for recycling, there is generally a mixture of all types of waste paper collected. Accordingly, in order to ensure that quality recycled copier and laser print paper are obtained, it is necessary to ensure that only laser and xerographic printed paper or paper products should be present. Secondly, it is necessary to ensure, as far as possible, the complete removal of ink from the pulped laser and xerographic printed papers in order to eliminate both the darkening effect produced by small particles of ink and the spot formation produced by larger pieces of ink. In view of the fact that the above-identified chemical techniques have not proved economically successful, having regard to the fact that firstly the waste paper cannot be properly separated, coupled with the fact that when laser and xerographic printed papers are treated then substantially complete ink removal is not obtained, in order to obtain the required good quality fibre, virgin pulp is being used which means that more and more trees have to be felled with consequent ecological problems associated therewith. It is an object of the present invention to provide a method for initially sorting high quality laser and xerographic printed paper waste from other paper waste and thereafter to remove ink therefrom in order to provide high brightness paper which is spot free. It is also a further object of the present invention to utilise the method of the present invention in the treatment of other types of printed paper products, wherein the ink utilised for printing has been appropriately treated. The present invention is based on the discovery that the ink utilised in laser and xerographic printed papers is comprised of a thermoplastic resin (usually PVC) containing carbon black as pigment and usually ferric oxide to assist in handling the dry ink in the printing device. Based on such discovery, we have now found that it is possible to separate laser and xerographic printed papers from other type of papers by magnetic separation and furthermore, have discovered it is possible to separate ink from the fibre of such laser and xerographic printed papers after pulping, again by the use of a magnet. According to one aspect of the present invention there is provided a method of dry separating and/or sorting laser and xerographic printed paper waste containing ink with a magnetic component from other paper waste products containing ink but which does not contain any magnetic material, by the use of at least one magnet and by applying an appropriate magnetic force. In such aspect of the invention, any suitable magnet may be utilised although same should be sufficiently strong in order to separate the paper containing ink with a magnetic component from paper containing ink but without such magnetic component. Suitable magnets would be an electromagnet, a permanent magnet or a superconducting magnet. In a preferred procedure in accordance with such aspect, a mixture of paper waste products would be allowed to fall substantially vertically past at least one operating magnet and the paper waste containing ink with a magnetic component would be magnetically drawn to one side and collected. Any suitable procedure can be adopted in this regard. The operating magnet(s) should apply a magnetic force over a large area of the body of paper being treated. Magnetic force is a function of two variables: 1) Magnetic flux density; and 2) Field gradient. Magnetic flux density is the product of magnetic field strength (or intensity) and permeability of a material. The magnetic field strength (intensity) is the magnitude of the field strength vector in a medium (i.e. the magnetic strain produced by neighbouring magnetic elements or current-carrying conductors) . It is believed that this aspect of the present invention would be of benefit to waste paper merchants or in mills which wish to select the particular type of paper for one particular operation in the mill, for example, production of recycled paper suitable for laser or xerographic copier paper. The residual paper could then be used for production of a lower grade of recycled paper. We have carried out tests in connection with laser and xerographic printed papers and have ascertained that same are susceptible to removal by a magnetic field. In accordance with the above aspect of the invention, we have been able to pick up paper having xerographic and laser print thereon. Accordingly, given a sheet with xerographic or laser print on it in a strong magnetic field then same will move towards a magnet and such procedure could be used as a means of preselecting xerographic or laser printed paper from office waste in the situation where there is a mixture of conventional waste material and xerographic waste material. Suitable magnetic forces are achieved by utilising background magnetic fields in excess of 4000 Gauss (4 tesla) and a field gradient in excess of 1000 Gauss/cm (10 tesla/m) . However, such high and absolute fields are not necessary to practice the invention. A high gradient magnetic separation device can be envisaged which will not require such high input field strengths. It is the magnetic field gradient that is important to effect the separation. There are several types of high gradient machine designs. These devices have been called "induced pole" devices. Suitable devices in this connection are for example:- Frantz Ferrofilter Carpco Separator Jones Separator Kolm-Marston separator suitably modified for utilisation with pulping techniques. Further tests have been carried out in connection with suspending the ink utilised in xerographic and laser printed papers in water using a surfactant due to the fact that the ink is hydrophobic. We have been able to recover such ink using a magnet. According to a further aspect of the present invention there is provided a method of removing magnetic ink from pulp stock formed from xerographic and laser printed paper waste to provide high brightness paper which is spot free, comprising feeding such pulped paper waste past at least one magnet for removal of all or substantially all of such magnetic ink. Assuming all the print is xerographic (there may be some conventional printing on the paper such as headings, logos etc.), then such method would allow for recycling of the ash present in the paper as well as the fibre, thereby increasing the yield. Additionally, if the ink which is normally melted on to the paper has not separated fully from the fibre of the paper after treatment in the pulper, then those fibres with ink still attached thereto would also be removed with such ink by the magnet(s) . Accordingly, the spot removal efficiency is improved since when recycling paper to produce high quality paper one does not require bits of fibre which have ink attached thereto. The arrangement of the at least one magnet will be so designed in order to exert a magnetic force comprising a background magnetic field of preferably at least 4000 Gauss and a field gradient preferably of at least 1000 Gauss/cm. Preferably, a plurality of magnets are utilised and the pulp stock is fed along an elongate channel-type container housing. The magnetic force is presented to the pulp in such a way that it will allow small magnetic particles to be captured or deflected. We have discovered that incredibly fine particle magnetic separation can be obtained by presenting the appropriate magnetic force to virtually every magnetic particle. The magnetic force applied must be sufficiently high and strong to overcome the fluid drag as the pulp is fed along the elongate housing. We have also discovered that by application of a very strong magnet to the outside of the wall of a beaker containing pulp, then it is possible to drag the magnetic particles to the inside of the wall of the beaker. Thus, in order to recover magnetic material from the pulp, it is possible to utilise a capture-type system wherein the magnets are dropped into the pulp or are located adjacently above the pulp. Alternatively, it is possible to utilise a deflection-type system wherein the magnets are located adjacent the outer walls of the channel-shaped housing and a sufficiently large magnetic force is applied to drag the magnetic particles to the inner walls of the channel-shaped housing. It is also possible to utilise a plurality of steel balls of selected size and shape, which balls are magnetised and thereafter introduced into the pulp. Magnetic particles and the like will become attached to the steel balls which may then be recovered from the pulp and de-magnetised, whereupon the metallic particles will become detached therefrom. The steel balls can thereafter be magnetised again and the above described process be carried out again. By utilising the procedures outlined above, separation of magnetic material for the pulp may be achieved. However the binders, fillers and white pigments contained in the pulp are not separated and therefore can be reused in producing recycled paper. It is necessary to overcome gravity and fluid drag forces (intensity of pulp) when utilising the magnetic separation system in accordance with the present invention. Savings can be achieved in that previously utilised separation procedures in procedures for recycling paper which involve costly materials, e.g. china clay, can be avoided. In a further aspect of the present invention, a method is provided for improving the recyclability of paper waste having ink thereon which does not normally contain a magnetic component, by utilising one or more magnetic carriers in the formulations of the printing ink utilised, to enable same to be removed by use of at least one magnet in accordance with the procedures outlined above. In this aspect of the invention, where carbon black is the primary pigment, it is possible to incorporate in such ink metallic iron or its oxides or some other paramagnetic material in order to make the ink magnetic. Such process would facilitate the removal of other types of inks such as flexographic inks were the carrier matrix is an alkali soluble polymer (polyacrylate) . In a still further aspect of the present invention there is provided a method of enabling adhesive material to be removed from paper pulp containing same, by incorporating a magnetic filler or carrier in said adhesive and removing such adhesive by magnetic means. Thus, adhesive can be removed from the water phase after pulping of paper containing adhesive used in the book binding field. It will thus be seen that the present invention contemplates the use of a magnet of suitable strength to enable a particular type of printed paper to be separated from other types of paper and for ink contained on such paper to be removed during the pulping process, both processes utilising a magnet such as an electromagnet, a permanent magnet or a superconducting magnet. It is also envisaged within the present invention to incorporate one or more magnetic carriers or fillers into other types of inks and adhesive or materials utilised in the paper manufacturing industry, so as to enable such inks and other types of materials to be removed from the paper pulp when recycling is taking place, again by magnetic means. The use of a magnet would be economic as compared to known processes and would be ecologically friendly in that no chemicals are being utilised. In view of the believed advantages obtained utilising such magnetic techniques, the amount of virgin pulp which would be required could be substantially reduced. As indicated above, any suitable ' magnet can be utilised providing same has sufficient field strength and intensity of field force. It is believed that a power of 10-20 kw would be sufficient to enable magnetic particles and the like to be removed as required.

Claims: CLAIMS 1. A method of dry separating and/or sorting laser and xerographic printed paper waste containing ink with a magnetic component from other paper waste products containing ink but which does not contain any magnetic material, by the use of at least one magnet and by applying an appropriate magnetic force. 2. A method as claimed in claim 1, in which at least one electro-magnet and/or at least one permanent magnet and/or at least one superconducting magnet is utilised. 3. A method as claimed in claim 1 or 2, in which a mixture of paper waste products comprising laser and xerographic printed paper waste containing ink with a magnetic component and other paper waste not containing such magnetic component, are allowed to fall substantially vertically past at least one operating magnet, the paper waste containing ink with a magnetic component being magnetically drawn to one side and collected, the paper waste not containing such magnetic component falling past said magnet(s) and not being attracted thereby. 4. A method as claimed in claim 1, 2 or 3, wherein the required magnetic forces are achieved by utilising background magnetic fields in excess of 4000 Gauss and a field gradient in excess of 1000 Gauss/cm. 5. A method of removing magnetic ink from pulp stock formed from xerographic and laser printed paper waste, comprising feeding such pulped paper waste past at least one magnet for removal of all or substantially all of such magnetic ink. 6. A method as claimed in claim 5, in which a plurality of magnets are utilised and the pulp stock is fed along an elongate channel-type container housing, the magnetic force being presented to the pulp in such a way that it will allow small magnet particles to be captured or deflected. 7. A method as claimed in claim 6, in which recovery of magnetic material from the pulp stock is effected in a capture-type manner, wherein the or each magnet is dropped into the pulp or is located adjacently above the pulp. 8. A method as claimed in claim 6, in which the magnetic material is recovered from the pulp in a deflection-type manner, wherein the or each magnet is located adjacent the outer wall of the channel-shaped housing. 9. A method as claimed in any one of claims 5 to 8, wherein at least one electromagnet and/or at least one permanent magnet and/or at least one superconducting magnet is utilised. 10. A method as claimed in any one of claims 5 to 9, wherein the arrangement of the at least one magnet is so designed in order to exert a magnetic force comprising a background magnetic field of at least 4000 Gauss and a field gradient of at least 1000 Gauss/cm. 11. A method for improving the recyclability of paper waste having ink thereon, which ink does not normally contain a magnetic component, by utilising one or more magnetic carriers in the formulation of the printing ink utilised, to enable same to be removed by use of at least one magnet in accordance with a method as claimed in any preceding claim. 12. A method as claimed in claim 11 wherein, where carbon black is the primary pigment of the ink, metallic iron or its oxides or some other paramagnet material is utilised in order to make the ink magnetic. 13. A method of enabling adhesive material to be removed from paper pulp containing same, comprising incorporating a magnetic filler or carrier in said adhesive and thereafter removing such adhesive by magnetic means.

Inventors: OWEN DAVID, OWEN, DAVID
Applicants: DOTSPEC LTD, OWEN DAVID, DOTSPEC LIMITED, OWEN, DAVID
Application year: 1994
Main classification: D21C5
IPC codes: B03C1, C09D11, C09J5, D21B1, D21C5